Methods and systems for determining viscosity of photo-curing resin for vat photopolymerization printer

Abstract

Methods and systems for forming 3D articles by vat photopolymerization processes in which resin viscosities are determined both prior to the commencement of the build process and, optionally, during the build process by measuring the torque required to raise and lower a build plate within the resin in the vat. The resin may be heated, and its viscosity thereby altered, by heating the resin in the vat using a light engine employed for fabricating the 3D articles.

What is claimed is: 
     
       1. A method for determining viscosity of a photo-curing resin used in a vat photopolymerization printer, said method comprising, prior to commencing a build process using the vat photopolymerization printer:
 filling a tank of the vat photopolymerization printer with resin and lowering a build plate of the vat photopolymerization printer into the resin; 
 engaging a motor to raise the build plate within the resin, and recording a first measure of a first torque required to raise the build plate by a torque meter; and 
 referencing, using the first measure of the torque, a table that tabulates measures of torque with known viscosities of resins to determine a first viscosity of the resin in the tank of the vat photopolymerization printer. 
 
     
     
       2. The method of  claim 1 , wherein the torque meter is integral to the motor and is configured to convert the first measure of the first torque into an electrical signal. 
     
     
       3. The method of  claim 1 , wherein the torque meter includes a rotary torque sensor that is in-line with a lead screw adapted to raise and lower the build plate under action by the motor. 
     
     
       4. The method of  claim 3 , wherein the rotary torque sensor comprises an optical or surface acoustic wave (SAW) torque sensor. 
     
     
       5. The method of  claim 1 , wherein the controller is, in part, configured as the torque meter. 
     
     
       6. The method of  claim 1 , wherein when the first measure of the first torque is between two tabulated values of resin viscosity in the table, determining the first viscosity of the resin in the tank of the vat photopolymerization printer as a nearest tabulated value of viscosity for the first measure of the first torque. 
     
     
       7. The method of  claim 1 , wherein when the first measure of the first torque is between two tabulated values of resin viscosity in the table, determining the first viscosity of the resin in the tank of the vat photopolymerization printer as an interpolated value of viscosity for the first measure of the first torque. 
     
     
       8. The method of  claim 1  further comprising, during the build process:
 determining a second viscosity of the resin in the tank of the vat photopolymerization printer by raising and/or lowering the build plate in the resin using the motor; 
 recording a second measure of a second torque required to raise and/or lower the build plate by the torque meter; and 
 determining, using the table look up, the second viscosity of the resin in the tank from the second measure of the second torque. 
 
     
     
       9. A system for determining viscosity of a photo-curing resin used in a vat photopolymerization printer, the system comprising the vat photopolymerization printer having a tank configured to hold a volume of resin; a build plate configured to be raised and lowered within the tank; a motor coupled to raise and/or lower the build plate; a torque meter configured to measure a torque required to raise the build plate in the resin; and a controller configured to operate said motor to raise and/or lower the build plate in the resin, to receive said measure of the torque from said torque meter, and to determine a viscosity of the resin in the tank of the vat photopolymerization printer by referencing, using the measure of the torque, a table that tabulates measures of torque with known viscosities of resins. 
     
     
       10. The system of  claim 9 , wherein the torque meter is integral to the motor and is configured to convert torque into an electrical signal. 
     
     
       11. The system of  claim 9 , wherein the torque meter includes a rotary torque sensor that is in-line with a lead screw coupled to raise and lower the build plate under action by the motor. 
     
     
       12. The system of  claim 11 , wherein the rotary torque sensor comprises an optical or surface acoustic wave (SAW) torque sensor. 
     
     
       13. The system of  claim 9 , wherein the controller is, in part, configured as the torque meter. 
     
     
       14. The system of  claim 9 , wherein the controller is further configured to determine the viscosity of the resin in the tank of the vat photopolymerization printer as a nearest tabulated value of viscosity for the measure of the torque when the measure of the torque is between two tabulated values of resin viscosity in the table. 
     
     
       15. The system of  claim 9 , wherein the controller is further configured to determine the viscosity of the resin in the tank of the vat photopolymerization printer as an interpolated value of viscosity for the measure of the torque when the measure of the torque is between two tabulated values of resin viscosity in the table.